The present invention relates to an auxiliary light emitting device used in a focusing condition detecting device for emitting an auxiliary light to an object, when a focusing condition is detected.
Conventionally, focusing condition detecting devices for detecting a focusing condition of a photographing lens with respect to an object are known. There are also proposed various cameras having an AF (automatic focusing) mechanism for achieving an in-focus condition by driving the focusing lens of the cameras in accordance with the detection result of the focusing condition detecting device. Although there are known various methods of detecting a focusing condition, a phase difference method is in particular widely used, among the various methods, by single-lens reflex cameras and the like as a method of obtaining a relatively accurate result over a wide range of a distance to an object.
The phase difference method of detecting a focusing condition by receiving a light ray from the object cannot detect a phase difference when an object is relatively dark, or when an object has a low contrast even if it is sufficiently bright. Accordingly, in such a situation, the focusing condition cannot be detected.
To cope with this problem, conventionally, there has been known an auxiliary light emitting device for emitting a light ray having a predetermined pattern towards an object when a focusing condition is detected using the phase difference method. The auxiliary light emitting device projects light having a specific pattern corresponding to an AF sensor for receiving light from the object. The pattern reflected by the object is received by the light receiving surface of an AF sensor as a pair of images through the optical system, and integrated by the AF sensor.
The focusing condition detecting device detects a defocus amount, i.e., the position of the image plane of the object on which the pattern is projected with respect to a film surface (or to a plane located at an equivalent to the film surface) based on an image signal corresponding to the pair of images received by the AF sensor by the phase difference method. Then an AF calculation is performed in order to determine the driving amount of a focusing lens so that the image plane of the object on which the pattern is projected coincides with the film surface.
A focusing condition is detected with respect to each of several focusing condition detecting areas assigned in a finder field, and the focusing lens is driven in accordance with a predetermined algorithm based on a result of a focusing condition detection process with respect to the plurality of AF areas.
FIG. 11 shows an example of the AF areas assigned in a finder field. In FIG. 11, a finder field 71 includes three AF areas 71L, 71C and 71R arranged approximately in an H-shape. AF sensors are arranged in correspondence to these AF areas 71L, 71C and 71R and detect focusing conditions according to the phase difference method by receiving light rays from an object in the respective AF areas 71L, 71C and 71R. Note, a light receiving element such as a CCD or the like is used as an AF sensor.
Next, an auxiliary light pattern will be described. When an object has a low contrast, light patterns as shown in FIG. 12 are projected to the object. That is, a first pattern P1 having a plurality of lines extending in an upward to downward direction in FIG. 12 is projected towards an area corresponding to the AF area 71C, and second patterns P2 each composed of a plurality of lines extending in a right to left direction in FIG. 12 are projected towards areas corresponding to the AF areas 71L, 71R. With this operation, a focusing condition of an object in the AF area 71C is detected by an AF sensor corresponding to the AF area 71C, and focusing conditions of objects corresponding to the AF areas 71L and 71R are detected by the AF sensors corresponding to these areas.
However, if the camera is of a lens-exchangeable type and/or if the photographing lens is a zoom lens, the focal length of the lens may change. When the focal length of a photographing lens increases, the range of the object covered by a finder field 71 is made relatively small as compared with a case in which the photographing lens has a short focal length. Since the magnification of an auxiliary light ray is unchanged in general, in a camera provided with a zoom lens, for example, even if the relationship between the respective AF areas 71L, 71C and 71R and the first and second light patterns P1, P2 is as shown in FIG. 12 when the zoom lens is located at a wide extremity, the movement of the zoom lens to a telephoto extremity changes the relationship therebetween as shown in FIG. 13. That is, since the focal length of the photographing lens increases, the area of the object covered by the finder field 71 is relatively narrowed, and as a result, objects viewed in all the AF areas 71L, 71C and 71R are illuminated with the light pattern P1 and the light patterns P2 are located outside of the AF areas 71L and 71R.
It is preferable for the detection of a focusing condition that a pattern generates a plurality of peaks (portions having a large quantity of light rays) along a direction in which an AF area extends. Therefore, when the relationship as shown in FIG. 13 is established between the AF areas 71L, 71C, 71R and the light patterns P1, P2, a focusing condition can be normally detected as to the AF area 71C, but, for the AF areas 71L and 71R, it is probable that the detection results are inaccurate.
In view of the above problems, it is an object of the present invention to provide an auxiliary light emitting device capable of emitting light rays having a plurality of patterns within respective AF areas even if the angle of view is changed as the focal length of the photographing lens changes and a region of the object whose focusing condition is to be detected is changed, and to provide a focusing condition detecting device using the above light emitting device.